WO2015137618A1

WO2015137618A1 - Method and apparatus for transmitting frame in wireless lan

Info

Publication number: WO2015137618A1
Application number: PCT/KR2015/000634
Authority: WO
Inventors: 최진수; 천진영; 이욱봉; 임동국; 조한규
Original assignee: 엘지전자 주식회사
Priority date: 2014-03-11
Filing date: 2015-01-21
Publication date: 2015-09-17
Also published as: EP3119154B1; EP3119154A4; EP3119154A1; US20170027001A1; US9924541B2; KR101901450B1; KR20160125417A

Abstract

Disclosed are a method and an apparatus for transmitting a frame in a wireless LAN. The method for transmitting a frame in a wireless LAN may comprise: a step in which an AP transmits an RTS frame for protecting a medium to an STA; a step in which the AP receives a CTS frame from the STA in response to the RTS frame; and a step in which the AP transmits a data frame to the STA in response to the CTS frame, wherein the RTS frame is included in a first PPDU which is generated on the basis of a first IFFT size, the data frame is included in a second PPDU which is generated on the basis of a second IFFT size, the second IFFT size is greater than the first IFFT size, and the data frame can be transmitted on the basis of a transmission-range-determining parameter which is determined on the basis of the difference between the second IFFT size and the first IFFT size.

Description

Method and apparatus for transmitting frame in WLAN

The present invention relates to wireless communication, and more particularly, to a method and apparatus for transmitting a frame in a WLAN.

The channel bandwidth available in the existing WLAN system has been varied from 20MHz to 160MHz. Accordingly, determining an appropriate channel bandwidth for communication between the transmitting terminal (station (STA)) and the receiving terminal has become an important factor in determining the performance of the WLAN system.

In order to determine an appropriate channel bandwidth for communication between a transmitting terminal and a receiving terminal, a dynamic channel bandwidth setting protocol based on a request to send (RTS) frame and a clear to send (CTS) frame has been developed from IEEE 802.11ac. Early RTS frames and CTS frames were designed to reduce hidden node problems and data frame collision overhead. The transmitting terminal transmits the RTS frame to the receiving terminal before transmitting the data frame. The destination terminal receiving the RTS frame responds to the transmitting terminal in the CTS frame. The third terminals receiving the RTS frame and the CTS frame may delay the medium access for a predetermined time in order to protect data frames to be transmitted later.

In the dynamic channel bandwidth setting protocol supported from IEEE 802.11ac, a transmitting terminal transmits an RTS frame in a wide bandwidth exceeding a 20 MHz channel bandwidth, and a target terminal can respond to a CTS frame according to a channel bandwidth currently available to it. have. For example, if the transmitting terminal wants to use the 160MHz channel bandwidth, it transmits the RTS frame in 160MHz channel bandwidth. If the channel bandwidth currently available in the target terminal is 80MHz, the target terminal transmits the CTS frame in the 80MHz channel bandwidth. When a transmitting terminal transmitting an RTS frame receives a CTS frame with a channel bandwidth of 80 MHz, a data frame subsequently transmitted by the transmitting terminal to a target terminal should be less than or equal to an 80 MHz channel bandwidth.

An object of the present invention is to provide a method for transmitting a frame in a WLAN.

Still another object of the present invention is to provide an apparatus for performing a method of transmitting a frame in a WLAN.

Method for transmitting a frame in a wireless LAN according to an aspect of the present invention for achieving the above object of the present invention, the AP (access point) transmits a request to send (RTS) frame for media protection to the STA (station) And receiving, by the AP, a clear to send (CTS) frame from the STA in response to the RTS frame, and transmitting, by the AP, a data frame to the STA in response to the CTS frame. The RTS frame may be included in a first physical layer protocol data unit (PPDU) generated based on a first inverse fast fourier transform (IFFT) size, and the data frame may be generated based on a second IFFT size. 2 PPDUs, wherein the second IFFT size is larger than the first IFFT size, and the data frame is determined based on a difference between the second IFFT size and the first IFFT size. It can be transmitted based on the song range determination parameters.

An access point (AP) for transmitting a frame in a WLAN according to another aspect of the present invention for achieving the above object of the present invention is a radio frequency (RF) unit and a RF unit implemented to transmit or receive a radio signal. And a processor operatively coupled to the processor, wherein the processor transmits a request to send (RTS) frame for media protection to a station (STA), and a clear to send (CTS) frame in response to the RTS frame. May be implemented to transmit a data frame to the STA in response to the CTS frame, wherein the RTS frame may be configured based on a first inverse fast fourier transform (IFFT) size. physical layer protocol data unit), wherein the data frame is included in a second PPDU generated based on a second IFFT size, and the second IFFT size is the first IFFT. Greater than rise, the data frame can be transmitted in claim 2 wherein the IFFT size and the IFFT size claim 1 based on the transfer area determination parameters determined based on the difference.

By synchronizing the transmission range between the frames it is possible to reduce the collision between frames in the WLAN system.

1 is a conceptual diagram illustrating a structure of a wireless local area network (WLAN).

2 is a conceptual diagram illustrating a method of using an RTS frame and a CTS frame to solve a hidden node issue and an exposed node issue.

3 is a conceptual diagram illustrating a method of generating a high efficiency (HE) PPDU based on an increased inverse fast fourier transform (IFFT) according to an embodiment of the present invention.

4 is a conceptual diagram illustrating a collision between frames due to a difference between a transmission range of a legacy frame and a transmission range of an HE frame.

5 is a conceptual diagram illustrating an MCS-based transmission range synchronization method according to an embodiment of the present invention.

6 is a conceptual diagram illustrating a transmission range synchronization method based on a CCA threshold according to an embodiment of the present invention.

7 is a conceptual diagram illustrating a transmission range synchronization method based on transmission power according to an embodiment of the present invention.

8 is a conceptual diagram illustrating a frame for transmission range synchronization according to an embodiment of the present invention.

9 is a conceptual diagram illustrating a HE PPDU format according to an embodiment of the present invention.

10 is a block diagram illustrating a wireless device to which an embodiment of the present invention can be applied.

1 shows the structure of the infrastructure basic service set (BSS) of the Institute of Electrical and Electronic Engineers (IEEE) 802.11.

Referring to the top of FIG. 1, the WLAN system may include one or more infrastructure BSSs 100 and 105 (hereinafter, BSS). The BSSs 100 and 105 are a set of APs and STAs such as an access point 125 and a STA1 (station 100-1) capable of successfully synchronizing and communicating with each other, and do not indicate a specific area. The BSS 105 may include one or more joinable STAs 105-1 and 105-2 to one AP 130.

The BSS may include at least one STA, APs 125 and 130 for providing a distribution service, and a distribution system (DS) 110 for connecting a plurality of APs.

The distributed system 110 may connect several BSSs 100 and 105 to implement an extended service set (ESS) 140 which is an extended service set. The ESS 140 may be used as a term indicating one network in which one or several APs 125 and 230 are connected through the distributed system 110. APs included in one ESS 140 may have the same service set identification (SSID).

The portal 120 may serve as a bridge for connecting the WLAN network (IEEE 802.11) with another network (for example, 802.X).

In the BSS as shown in the upper part of FIG. 1, a network between the APs 125 and 130 and a network between the APs 125 and 130 and the STAs 100-1, 105-1 and 105-2 may be implemented. However, it may be possible to perform communication by setting up a network even between STAs without the APs 125 and 130. A network that performs communication by establishing a network even between STAs without APs 125 and 130 is defined as an ad-hoc network or an independent basic service set (BSS).

1 is a conceptual diagram illustrating an IBSS.

Referring to the bottom of FIG. 1, the IBSS is a BSS operating in an ad-hoc mode. Since IBSS does not contain an AP, there is no centralized management entity. That is, in the IBSS, the STAs 150-1, 150-2, 150-3, 155-4, and 155-5 are managed in a distributed manner. In the IBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may be mobile STAs, and access to a distributed system is not allowed, thus making a self-contained network. network).

A STA is any functional medium that includes medium access control (MAC) conforming to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard and a physical layer interface to a wireless medium. May be used to mean both an AP and a non-AP STA (Non-AP Station).

The STA may include a mobile terminal, a wireless device, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile subscriber unit ( It may also be called various names such as a mobile subscriber unit or simply a user.

Referring to FIG. 2, a short signal transmission frame such as a request to send (RTS) frame and a clear to send (CTS) frame to solve a hidden node issue and an exposed node issue ( short signaling frame) may be used. The neighboring STAs may know whether to transmit or receive data between the two STAs based on the RTS frame and the CTS frame.

2A illustrates a method of transmitting the RTS frame 203 and the CTS frame 205 to solve a hidden node issue.

It may be assumed that both STA A 200 and STA C 220 attempt to transmit a data frame to STA B 210. The STA A 200 may transmit the RTS frame 203 to the STA B 210 before transmitting the data frame, and the STA B 210 may transmit the CTS frame 205 to the STA A 200. STA C 220 may overhear the CTS frame 205 and may know transmission of the frame from STA A 200 to STA B 210 over the medium. The STA C 220 may set a network allocation vector (NAV) until the transmission of the data frame from the STA A 200 to the STA B 210 ends. By using this method, collision between frames due to hidden nodes can be prevented.

2B illustrates a method of transmitting the RTS frame 233 and the CTS frame 235 to solve the exposed node issue.

STA C 250 determines whether there is a collision when transmitting a frame to another STA D 260 based on the monitoring of the RTS frame 233 and the CTS frame 235 of STA A 230 and STA B 240. Can be.

STA B 240 may transmit an RTS frame 233 to STA A 230, and STA A 230 may transmit a CTS frame 235 to STA B 240. STA C 250 overhears only the RTS frame 233 transmitted by STA B 240 and fails to overhear the CTS frame 235 transmitted by STA A 230. Accordingly, STA C 250 may know that STA A 230 is outside the carrier sensing range of STA C 250. Accordingly, STA C 250 may transmit data to STA D 260.

The RTS frame format and the CTS frame format are disclosed in 8.3.1.2 RTS frame format and 8.3.1.3 CTS frame format of IEEE P802.11-REVmc ™ / D2.0, October 2013.

There is an increasing demand for improving throughput and quality of experience (QoE) over existing WLAN systems (legacy WLAN systems), and the introduction of new frame (or PPDU) formats for new WLAN systems is being discussed. When a new frame (PPDU) format is introduced, a legacy frame (PPDU) format and a new frame (PPDU) format for a legacy STA operating in an existing legacy WLAN system may coexist.

The legacy STA may not know whether or not the new WLAN system is operated. Therefore, there is a need to design a new WLAN system so that there is no or minimal impact on performance for the legacy STA. In addition, due to consideration of performance degradation for the legacy STA, it is not desirable that the gain that the new WLAN system can take is unnecessarily reduced. Therefore, it is necessary to design a new WLAN system by properly balancing the gain of the new WLAN system and the performance degradation of the legacy WLAN system.

In FIG. 3, an FFT / IFFT method for generating an HE PPDU is disclosed.

The HE PPDU may be divided into a legacy part 300 up to L-SIG (legacy-signal) and an HE part 320 after the L-SIG. The legacy portion 300 may include information for the operation of the legacy STA. The HE portion 320 includes an HE field for supporting operations on a WLAN system such as high efficiency (SIG) -SIG, short training field (HE-STF), long training field (HE-LTF), and HE-SIG2. can do. This HE field is an example of a field for interpreting the HE PPDU except for the legacy part. The HE field will be described later in detail.

As described above, in order to reduce the effects of large delay spreads in the outdoor environment, there is an IFFT option (or other IFFT size, increased IFFT size) different from the legacy IFFT size applied to the legacy part. Can be used for the generation of The HE portion 320 may be generated based on an IFFT (increased IFFT size) of a relatively larger size than the legacy portion 300 based on the same bandwidth size. In this case, different numerologies (eg, guard interval (GI) size, IFFT size) may be used for generation of the HE PPDU.

Referring to FIG. 3, the increase IFFT size (eg, 512IFFT) used for the HE portion 320 in the HE PPDU is twice the legacy IFFT size (eg, 256IFFT) used for the legacy portion 300. Is disclosed.

When the IFFT size is doubled, the number of subcarriers can be doubled and the subcarrier spacing can be reduced by half on the same bandwidth. In addition, the length of the effective symbol duration may also be doubled and if the GI portion is the same (eg, 1/4), the length (or duration) of the GI may be doubled. One OFDM symbol may include a valid symbol and a GI. That is, the total symbol duration, which is the duration of one OFDM symbol, may be the sum of the effective symbol duration and the GI duration.

As another example, when the IFFT size is increased by four times, the number of subcarriers can be increased by four times, the subcarrier space can be reduced by one quarter times, and the length of the effective symbol duration can be increased by four times. If the GI potions are the same, the length of the GI may increase by four times.

When the length of the GI is relatively long, the effects of inter symbol interference (ISI) and inter carrier interference (ICI) due to large delay spread can be relatively reduced. Therefore, as the length of the GI increases, the transmission range of the PPDU (or a frame included in the PPDU) may increase.

If the GI portion decreases (eg, 1/4 to 1/16), the length of the GI may increase less than the rate of increase of the IFFT size. In this case, the radio resource utilization efficiency may increase.

The HE STA should be able to perform decoding on the legacy portion 300 generated based on the legacy IFFT size included in the PPDU and the HE portion 320 generated based on the increased IFFT size. On the other hand, the legacy STA may decode the legacy portion 300, but may not decode the HE portion 320. Hereinafter, in the embodiment of the present invention, the HE STA may indicate a STA capable of decoding the HE PPDU including the HE portion 320 generated based on the increased IFFT size. The legacy STA may indicate a STA capable of decoding the legacy portion generated based on the legacy IFFT size but unable to decode the HE portion 320 generated based on the increased IFFT size. The HE AP may indicate an AP capable of supporting both the HE STA and the legacy STA.

In addition, in the following embodiment, the HE PPDU is a PPDU generated based on an incremental IFFT (or legacy IFFT and an incremental IFFT), and the legacy PPDU may indicate a PPDU generated based only on the legacy IFFT. In addition, a frame transmitted through the HE PPDU (eg, a data frame) may be expressed in terms of a HE frame, and a frame delivered through a legacy PPDU may be referred to as a legacy frame (eg, an RTS frame or a CTS frame).

The HE PPDU disclosed in FIG. 3 may be used for transmission or reception of a data frame (or management frame) between the HE STA and the HE AP.

RTS frames and CTS frames should be able to be detected and decoded by legacy STAs as well as legacy STAs. Thus, the format of the RTS frame and the CTS frame (or the RTS PPDU carrying the RTS frame and the CTS PPDU carrying the CTS frame) needs to maintain the legacy frame (or legacy PPDU) format. Accordingly, the RTS frame and the CTS frame may be included in the legacy PPDU and transmitted.

Due to the difference in the IFFT size, the transmission range of the data PPDU (or data frame) and the transmission range of the RTS PPDU (RTS frame) / CTS PPDU (CTS frame) may vary. The non-target STA located within the transmission range of the RTS frame and the CTS frame may receive the RTS frame and the CTS frame and set a network allocation vector (NAV). The non-target STA may indicate a HE STA or a legacy STA that is not a sender or receiver of the RTS frame or CTS frame. However, the non-target STA located outside the transmission range of the RTS frame and / or the CTS frame may not receive the RTS frame and / or the CTS frame. The non-target STA that has not received the RTS frame and / or the CTS frame may perform channel access during communication between the AP and the target STA to transmit the frame to the AP. When the non-target STA transmits a frame, a frame transmitted from the target STA to the AP (or a frame transmitted from the AP to the target STA) and the frame transmitted by the non-target STA may collide.

That is, a collision between frames may occur due to a difference between the transmission range of the RTS frame / CTS frame and the transmission range of the HE frame transmitted through the HE PPDU generated based on the increased IFFT size.

Hereinafter, in an embodiment of the present invention, collision between frames in a BSS is reduced by reducing a difference between a transmission range of an RTS frame / CTS frame transmitted through a legacy PPDU and a transmission range of a frame (eg, a data frame) transmitted through an HE PPDU. A method for preventing this is disclosed. A method of reducing the difference between the transmission range of the RTS frame / CTS frame and the transmission range of the HE frame transmitted through the PPDU generated based on the increased IFFT size may be expressed by the term transmission range synchronization method.

Hereinafter, a frame transmitted through the HE PPDU generated based on the increased IFFT size is assumed to be a data frame.

In FIG. 4, a collision between frames occurring in a BSS is started due to a difference between a transmission range of an RTS frame / CTS frame and a transmission range of a data frame. It is assumed that the RTS frame / CTS frame is included in the legacy PPDU and transmitted, and the data frame is included in the HE PPDU.

Referring to FIG. 4, the HE AP 400 may support L-STA1 410 and L-STA2 420 which are legacy STAs capable of decoding legacy PPDUs. In addition, the HE AP 400 may also support the HE-STA 430 which is an STA capable of decoding the HE PPDU.

The transmission range of legacy frames (eg, RTS frames, CTS frames) of the HE AP 400 based on the HE AP 400 is legacy coverage, and the transmission range of HE frames (eg, data frames) is extended. It may be expressed in terms of coverage. For example, legacy coverage may be a transmission range of a legacy frame delivered through a legacy PPDU generated based on 64IFFT, and extended coverage may be a transmission range of a HE frame delivered through an HE PPDU generated based on 128IFFT.

L-STA1 410 may be located within legacy coverage, and L-STA2 420 and HE STA 430 may be located within extended coverage.

The HE AP 400 may transmit an RTS frame for communication with the HE-STA 430. The RTS frame can be transmitted within legacy coverage. The HE-STA 430 may be located in legacy coverage and may transmit the CTS frame to the AP in response to the RTS frame transmitted by the HE AP 400.

The L-STA1 410 located within the legacy coverage may perform detection for the RTS frame sent by the HE AP 400. Accordingly, the L-STA1 410 may receive the RTS frame and set the NAV, and may not attempt channel access in the transmission period of the data frame from the HE AP 400 to the HE-STA 430. The L-STA1 410 located in the legacy coverage does not cause a problem due to the interframe collision on the WLAN system.

L-STA2 420 may be located within extended coverage beyond legacy coverage. The L-STA2 420 may not receive the RTS frame transmitted by the HE AP 400 and cannot set an NAV based on the RTS frame. In addition, the L-STA2 420 may not receive the CTS frame transmitted by the HE-STA 430. In this case, the L-STA2 420 may transmit a frame by performing channel access on the communication interval between the HE AP 400 and the HE-STA 430, and collision between frames may occur within the BSS. In more detail, a collision may occur between a data frame transmitted from the HE AP 400 to the HE-STA 430 and a data frame transmitted from the L-STA2 420 to the HE AP 400.

On the communication interval between the HE AP 400 and the HE-STA 430, the transmission of the frame not only by the L-STA2 420 but also by other non-target STAs (for example, other HE STAs) is performed to perform a frame within the BSS. A conflict between them can occur. The non-target STA may be a hidden STA for the HE AP 400 or the target STA (HE-STA 430).

Modulation and coding scheme (MCS) based transmission range synchronization method, clear channel assessment (CCA) based transmission range synchronization method and transmission power in order to prevent collision between frames due to the difference in transmission range of legacy frame and HE frame. Based transmission range synchronization method may be used.

In FIG. 5, legacy frames (eg, RTS frames) and HE frames (eg, data frames) based on MCS indexes for legacy PPDUs (or legacy frames) and MCS indexes for HE PPDUs (or HE frames). A method of synchronizing transmission ranges for a is disclosed. As the MCS index is lowered relatively, an error-resistant modulation method and a coding rate may be used. As the MCS index is relatively high, a modulation method and a coding rate, which are relatively error tolerant, may be used. Table 1 below shows modulation methods and coding rates according to MCS indexes.

TABLE 1

Referring to FIG. 5, transmission range synchronization may be performed by differently setting an MCS index for transmitting the RTS frame 500 and an MCS index for transmitting the data frame 520.

Hereinafter, the MCS index for the RTS frame 500 may be expressed in terms of an RTS MCS index, and the MCS index for the data frame 520 may be a data MCS index.

The RTS MCS index may be set to a value relatively smaller than the data MCS index. When the RTS MCS index is set to a value relatively smaller than the data MCS index, the RTS frame 500 may be more error resistant than the data frame 520. If the RTS frame 500 is more robust to error than the data frame 520, if only the MCS index is considered without considering the IFFT size, the transmission range of the RTS frame 500 is based on the transmission range of the data frame 520. It can be relatively wider. The data frame 520 transmitted through the HE PPDU may have a relatively wider transmission range than the RTS frame 500 transmitted through the legacy PPDU. However, if the data MCS index is larger than the RTS MCS index, the possible transmission range can be reduced.

That is, by reducing the possible transmission range of the data frame 520 based on the constraints on the data MCS index that can be used for transmission of the data frame 520, the transmission range of the RTS frame 500 and the data frame 520 Synchronization between transmission ranges may be performed. The transmission range of the reduced data frame 520 based on the constraint on the MCS index may be an MCS limited data frame transmission range.

According to an embodiment of the present invention, the difference between the data MCS index and the RTS MCS index may be determined based on the difference between the transmission range of the data frame 520 of the HE AP and the transmission range of the RTS frame 500 of the HE AP. If the difference in the transmission range is x (dB), the difference between the data MCS index and the RTS MCS index may have a difference corresponding to x (dB). Various units may be used to indicate differences in transmission ranges. For convenience of explanation, a description will be given except for a unit indicating a difference in transmission range.

Hereinafter, the transmission range difference may indicate a difference between the transmission range of the data frame 520 of the HE AP and the transmission range of the RTS frame 500 of the HE AP, and the MCS index difference may indicate a difference between the data MCS index and the RTS MCS index. Can be.

The transmission range difference may be a parameter determined based on the increase in the IFFT size. For example, if the incremental IFFT size is twice as large as the legacy IFFT size, the transmission range difference may be 3 (dB) and if the incremental IFFT size is 4 times larger than the legacy IFFT size, the transmission range difference may be 6 (dB). . The transmission range difference may be adaptively changed according to parameters additionally considering the WLAN system environment.

The MCS index difference may be determined corresponding to the transmission range difference. For example, the transmission range difference 3 (dB) may correspond to the MCS index difference 2. That is, when the difference between the transmission range of the data frame 520 of the HE AP and the transmission range of the RTS frame 500 of the HE AP is 3 (dB), the data MCS index may be 2 larger than the RTS MCS index. Specifically, when the data MCS index is determined to be 2, the RTS MCS index may be determined to be 0.

For example, the AP may use the first MCS index determined for the transmission of the RTS frame 500 based on the feedback information received from the actual STA. In addition, the AP may use the increased second MCS index for transmission of the data frame 520 in consideration of the transmission range difference in addition to the first MCS index. The second MCS index may be determined by adding the MCS index difference determined based on the transmission range difference to the first MCS index.

Depending on the difference in the transmission range, some MCS indexes may not be used for transmission of the data frame 520. Table 2 below is a table showing the MCS index available for the transmission of the data frame 520.

TABLE 2

In Table 2, the MCS index difference according to the transmission range difference is 2. If the data MCS index is 0 or 1, the data MCS index cannot be larger than the RTS MCS index. Thus, the use of 0 or 1 as the data MCS index can be limited.

Table 2 is an MCS index table according to specific transmission range differences. The difference in transmission range may vary depending on the increasing IFFT size. Accordingly, the MCS index whose use as a data MCS index is restricted may vary according to the increase IFFT size (128IFFT, 256IFFT, 512IFFT, or 1024IFFT). That is, the table showing the MCS index available for the transmission of the data frame 520 may vary according to the increased IFFT size.

Although the transmission range of the data frame 520 may be partially reduced, the data rate may increase due to the high use of MCS. According to an embodiment of the present invention, the AP only shows a portion of STAs in the BSS that do not need to transmit the data frame 520 based on a low MCS index (eg, MCS index 0 and MCS index 1) in FIG. 5. In the MCS-based transmission range synchronization method described above may be used. For example, an AP may be located in a data frame 520 to STAs located at a BSS center or having a sufficient signal to noise ratio margin, rather than a STA located at a BSS edge requiring a low MCS. In transmission, MCS-based transmission range synchronization method may be used. In the WLAN system, one or more different MCS tables for supporting STAs operating in different environments may be used.

In the transmission of the CTS frame as well as the transmission of the RTS frame 500, the transmission may be performed using the same MCS index as that of the RTS frame 500. The HE STA receiving the CTS frame may transmit the CTS frame generated with the same MCS index as the MCS index used for the transmission of the RTS frame 500. For example, the MCS index for the transmission of the RTS frame 500 and the CTS frame may be 0, and the MCS index for the transmission of the data frame 520 may be 2. In addition, the MCS-based transmission range synchronization method may be applied for the transmission of the RTS frame 500, the CTS frame and the data frame 520, as well as the transmission of other legacy frames (or legacy PPDUs) and HE frames (HE PPDUs).

If the transmission of the frame is successful in the existing WLAN system, the subsequent frame among a plurality of frames transmitted or received within one transmission opportunity (TXOP) is equal to or lower than the MCS index used for transmission of the previous frame. It was transmitted based on the MCS index. In the MCS-based transmission range synchronization method according to an embodiment of the present invention, the MCS index of the data frame 520 transmitted after the transmission and reception of the RTS frame and the CTS frame is larger than the MCS index of the RTS frame 500 and the CTS frame. The transmission range difference may be additionally taken into consideration.

In FIG. 6, a CCA threshold for receiving a legacy PPDU (or a legacy frame) and a CCA threshold for receiving a HE PPDU (or an HE frame) are set differently, thereby transmitting an RTS frame 600 and a CTS frame, which are legacy frames. A method of synchronizing a range and a transmission range of a data frame 620 that is an HE frame is disclosed. The CCA threshold may be a minimum receiver sensitivity level defined in the WLAN system. When a frame transmitted with an intensity greater than or equal to the CCA threshold is sensed on the medium, the STA may determine that the medium is busy even when a frame is received (or decoded) or a pending frame is present and may not perform channel access. have. On the contrary, when a signal smaller than the CCA threshold is sensed on the medium, the STA may determine that the medium is idle and perform channel access when the frame is not received (or decoded) or when there is a frame bound to the STA.

When the CCA threshold is relatively large, the sensing sensitivity of the STA becomes relatively low, and only a frame transmitted with a relatively strong strength may be detected by the STA. That is, when the CCA threshold of the receiving STA is relatively large, the transmission range (or coverage) of the frame of the AP (or the frame reception range of the STA) may be reduced (or narrowed).

When the CCA threshold is relatively small, the sensing sensitivity of the STA becomes relatively high, and a frame transmitted with a relatively weak strength may also be detected by the STA. That is, when the CCA threshold of the receiving STA becomes relatively small, the transmission range (or coverage) of the frame of the AP (or the frame reception range of the STA) may be increased (or widened).

Referring to FIG. 6, when a CCA threshold for receiving an RTS frame 600 (or a legacy frame) of a receiving STA is determined (or set) to −82 dBm, reception of a data frame (or HE frame) of the receiving STA The CCA threshold for may be determined (or set) to a value greater than -82 dBm (eg, -79 dBm). In this case, considering only the CCA threshold, the transmission range of the data frame 620 may be relatively smaller than the transmission range of the RTS frame due to the CCA threshold of the receiving STA.

Hereinafter, the CCA threshold for the RTS frame 600 is an RTS CCA threshold, and hereinafter, the CCA threshold for the data frame 620 may be expressed by the term data CCA threshold.

The data CCA threshold and the RTS CCA threshold of the receiving STA may be set based on the difference in the transmission range due to the difference in the IFFT size. For example, when the transmission range difference is 3 (dB), the data CCA threshold may be set to be 3 (dB) larger than the RTS CCA threshold. As a specific value, when the RTS CCA threshold is set to −82 dBm, the data CCA threshold may be set to −82 dBm + 3 (dB) = − 79 dBm. If the data CCA threshold is set to −82 dBm as another value, the RTS CCA threshold may be set to −85 dBm. If the transmission range difference is changed due to the difference between the legacy IFFT size and the increasing IFFT size, the difference between the RTS CCA threshold and the data CCA threshold may also be different.

The CCA threshold for the RTS frame 600 may be determined so as not to affect the RTS frame detection performance of the legacy STA.

When the data CCA threshold is increased, the transmission range (or reception range) of the data frame 620 transmitted by the AP may be partially reduced. However, due to an increase in the data CCA threshold, the transmission opportunity of the receiving STA may be relatively increased. In more detail, when the data CCA threshold is increased, the media sensing sensitivity of the receiving STA may decrease to increase the time interval for viewing the media as relatively idle. Therefore, when the data CCA threshold is increased, the transmission opportunity of the receiving STA may be relatively increased.

The CCA thresholds for the CTS frames as well as the RTS frame 600 may be set to be the same as the RTS CCA thresholds. In addition, the transmission range difference may vary according to the increase IFFT size (128IFFT, 256IFFT, 512IFFT, or 1024IFFT), and the difference of the CCA value (difference between the data CCA threshold and the RTS CCA threshold) may vary according to the transmission range difference. . In a WLAN system, a difference between CCA values according to an increased IFFT size may be defined and used for setting a CCA threshold value of an STA in a BSS.

In FIG. 7, the transmission power for the legacy PPDU (or the legacy frame) and the transmission power for the HE PPDU (or the HE frame) are set differently so that the transmission range and the HE of the legacy frame, the RTS frame 700 and the CTS frame. A method of synchronizing the transmission range of a data frame 720 which is a frame is disclosed. Hereinafter, the transmission power for the transmission of the RTS frame 700 may be expressed in terms of the RTS transmission power and the transmission power for the transmission of the data frame 720 may be referred to as data transmission power.

The AP may determine the RTS transmission power and the data transmission power based on the power control method.

For example, when the RTS transmission power is 30 dBm, the data transmission power may be set to a value lower than 30 dBm. When the data transmission power is set to a value smaller than the RTS transmission power, considering only the transmission power, the transmission range of the data frame may be relatively smaller than the transmission range of the RTS frame.

In consideration of the transmission range difference, the RTS transmission power and the data transmission power may be set differently. For example, if there is a difference in transmission range by 3 (dB) due to the difference in the IFFT size and the RTS transmission power is set to 30 dBm, the data transmission power may be set to 27 dBm. The difference between the RTS transmission power and the data transmission power may vary depending on the transmission range difference.

Due to the limitation of the transmission power, the transmission range of the data frame 720 may be reduced. However, when the transmission power is reduced, interference to the peripheral BSS may be reduced. Therefore, the limitation of the transmission power can bring the improvement of the overall system performance.

The transmission range synchronization method based on the transmission power may be applied to the legacy frame (legacy PPDU) and the HE frame (HE PPDU). In this case, the transmission power for the transmission of the legacy frame is the legacy transmission power, for the transmission of the HE frame. The transmit power may also be expressed in terms of HE transmit power.

The transmission power for the CTS frame as well as the RTS frame 700 may be set to be the same as the RTS transmission power. The transmission range difference may vary according to the increasing IFFT size (128IFFT, 256IFFT, 512IFFT, or 1024IFFT), and the transmission power difference according to the transmission range difference (difference between RTS transmission power and data transmission power or difference between legacy transmission power and HE transmission power) ) May vary. In a WLAN system, a transmission power difference according to an increased IFFT size may be defined and used.

Transmission range synchronization methods based on MCS, CCA threshold, or transmission power disclosed in FIGS. 5 to 7 may be used individually or may be used in combination. For example, transmission range synchronization may be performed through control of at least two elements of the MCS, the CCA threshold, and the transmission power. Variables for determining a transmission range such as an MCS, a CCA threshold, or a transmission power may be expressed by the term transmission range determination parameter.

In more detail, the AP may transmit an RTS frame for medium protection to the STA, and the AP may receive a CTS frame from the STA in response to the RTS frame. In addition, the AP may transmit a data frame to the STA in response to the CTS frame. In this case, the RTS frame may be included in the first PPDU generated based on the first IFFT size, and the data frame may be included in the second PPDU generated based on the second IFFT size. The second IFFT size may be larger than the first IFFT size, and the data frame may be transmitted based on a transmission range determination parameter determined based on a difference between the second IFFT size and the first IFFT size.

The transmission range determination parameter may include a first MCS index for modulation and coding of a data frame. The first MCS index may be larger than the second MCS index for modulation and coding of the RTS frame.

In addition, the transmission range determination parameter may include a first CCA threshold for receiving a data frame. The first CCA threshold may be greater than the second CCA threshold for reception of the RTS frame.

In addition, the transmission range determination parameter may include a first transmission power for transmission of the data frame, and the first transmission power may be smaller than the second transmission power for transmission of the RTS frame.

Although it is assumed that a data frame is transmitted based on a transmission range determination parameter, an RTS frame may be transmitted based on a transmission range determination parameter (a second MCS index, a second CCA threshold, and a second transmission power).

In FIG. 8, a frame including information on an MCS index, a CCA threshold, or a transmission power for transmission range synchronization shown in FIGS. 5 to 7 is disclosed. A frame including information for transmission range synchronization may be expressed by the term transmission range synchronization frame.

In FIG. 8, for convenience of description, it is assumed that a transmission range synchronization frame includes all information on an MCS index, a CCA threshold value, or a transmission power. However, only information of at least one of the MCS index, the CCA threshold value, and the transmission power may be included in the transmission range synchronization frame as information for transmission range synchronization. For example, the transmission range synchronization frame includes only information on the CCA threshold, the STA receiving the information on the CCA threshold through the transmission range synchronization frame is CCA threshold for receiving the RTS frame based on the CCA threshold Values and CCA thresholds for receiving data frames may be set differently.

Referring to FIG. 8, the AP transmits a transmission range synchronization frame including information for synchronization between a transmission range of a legacy frame (eg, an RTS frame / CTS frame) and a transmission range of an HE frame (eg, a data frame). May be transmitted to the STA.

Information for synchronization between transmission ranges included in the transmission range synchronization frame may include an MCS setting field, a CCA threshold setting field, and a transmission power setting field.

The MCS setting field 800 may include information about an MCS index for an RTS frame (eg, a legacy frame) and / or information about an MCS index for a data frame (eg, an HE frame). When the STA receives the MCS configuration field 800 through the transmission range synchronization frame, the STA may determine the MCS index used for the transmission of the data frame except for the constant MCS index. In addition, the STA that receives the MCS configuration field 800 through the transmission range synchronization frame may transmit the CTS frame or data frame in consideration of the MCS index included in the MCS configuration field 800 when the CTS frame or data frame is transmitted. Can be.

The CCA threshold setting field 820 includes information about CCA thresholds for RTS frames (eg legacy frames) and / or information about CCA thresholds for data frames (eg HE frames). can do.

The transmit power setting field 840 may include information about transmit power for an RTS frame (eg, a legacy frame) and / or information about transmit power for a data frame (eg, an HE frame). . After receiving the transmission power setting field 840 through the transmission range synchronization frame, the STA may transmit the CTS frame or data frame in consideration of the transmission power information included in the transmission power setting field when the CTS frame or data frame is transmitted. .

The STA may receive a transmission range synchronization frame from the AP and set a CCA threshold. Alternatively, the STA may determine the MCS index and the transmission power of the CTS frame to be transmitted to the AP based on the transmission range synchronization frame.

That is, although the AP transmits a transmission range synchronization frame on a broadcast basis, the transmission range synchronization frame may include transmission range determination parameters (MCS index, CCA threshold, transmission power, etc.). The transmission range synchronization frame may be a newly defined frame or may be a beacon frame transmitted periodically by the AP.

In FIG. 8, it is assumed that information for transmission range synchronization is included in an MSDU, but information for transmission range synchronization may be included in a MAC header or a physical layer protocol data unit (PPDU) header (PHY header and / or PHY preamble). have.

4 to 8, the AP assumes the case of transmitting the RTS frame and the data frame. However, the embodiment disclosed in FIGS. 4 to 8 may be applied even when the STA transmits the RTS frame and the data frame. 4 to 8, the PPDU generated based on the IFFT is disclosed, but the PPDU may be generated based on an inverse discrete fourier transform (IDFT) instead of the IFFT.

9 illustrates a HE PPDU format according to an embodiment of the present invention.

The HE PPDU format may be used for transmission of an HE frame such as a data frame.

9, the PHY header of the downlink PPDU may include a legacy short training field (L-STF), a legacy long training field (L-LTF), a legacy-signal (L-SIG), and an HE-SIG A. (high efficiency-signal A), high efficiency-short training field (HE-STF), high efficiency-long training field (HE-LTF), and high efficiency-signal-B (HE-SIG B). From the PHY header to the L-SIG may be divided into a legacy part and a high efficiency (HE) part after the L-SIG.

The L-STF 900 may include a short training orthogonal frequency division multiplexing symbol. The L-STF 900 may be used for frame detection, automatic gain control (AGC), diversity detection, and coarse frequency / time synchronization.

The L-LTF 910 may include a long training orthogonal frequency division multiplexing symbol. The L-LTF 910 may be used for fine frequency / time synchronization and channel prediction.

L-SIG 920 may be used to transmit control information. The L-SIG 920 may include information about a data rate and a data length.

The HE-SIG A 930 may include information for indicating an STA to receive the PPDU. For example, the HE-SIG A 930 may include an identifier of a specific STA (or AP) to receive a PPDU, and information for indicating a group of the specific STA. In addition, the HE-SIG A 930 may also include resource allocation information for the STA when the PPDU is transmitted based on OFDMA or MIMO.

In addition, the HE-SIG A 930 may include color bit information, bandwidth information, tail bits, CRC bits, and MCS for the HE-SIG B 960 for BSS identification information. It may include modulation and coding scheme information, symbol number information for the HE-SIG B 960, and cyclic prefix (CP) (or guard interval (GI)) length information.

The HE-STF 940 may be used to improve automatic gain control estimation in a multiple input multiple output (MIMO) environment or an OFDMA environment.

The HE-LTF 950 may be used to estimate a channel in a MIMO environment or an OFDMA environment.

The HE-SIG B 960 may include information about a length MCS of a physical layer service data unit (PSDU) for each STA, tail bits, and the like. In addition, the HE-SIG B 960 may include information on an STA to receive a PPDU, OFDMA-based resource allocation information (or MU-MIMO information). When the HE-SIG B 960 includes OFDMA based resource allocation information (or MU-MIMO related information), the HE-SIG A 930 may not include resource allocation information.

The size of the IFFT applied to the field after the HE-STF 940 and the HE-STF 940 may be different from the size of the IFFT applied to the field before the HE-STF 940. For example, the size of the IFFT applied to the field after the HE-STF 940 and the HE-STF 940 may be four times larger than the size of the IFFT applied to the field before the HE-STF 940. The STA may receive the HE-SIG A 930 and may be instructed to receive the downlink PPDU based on the HE-SIG A 930. In this case, the STA may perform decoding based on the changed FFT size from the field after the HE-STF 940 and the HE-STF 940. On the contrary, if the STA is not instructed to receive the downlink PPDU based on the HE-SIG A 930, the STA may stop decoding and configure a network allocation vector (NAV). The cyclic prefix (CP) of the HE-STF 940 may have a larger size than the CP of another field, and during this CP period, the STA may perform decoding on the downlink PPDU by changing the FFT size.

The order of fields constituting the format of the PPDU disclosed at the top of FIG. 9 may vary. For example, the HE-SIG B 915 of the HE portion may be located immediately after the HE-SIG A 905, as disclosed in the interruption of FIG. 9. The STA may decode up to HE-SIG A 905 and HE-SIG B 915, receive necessary control information, and make NAV settings. Similarly, the size of the IFFT applied to the fields after the HE-STF 925 and the HE-STF 925 may be different from the size of the IFFT applied to the field before the HE-STF 925.

The STA may receive the HE-SIG A 905 and the HE-SIG B 915. When the reception of the PPDU is indicated based on the HE-SIG A 905, the STA may perform decoding on the PPDU by changing the FFT size from the HE-STF 925. Conversely, when the STA receives the HE-SIG A 905 and is not instructed to receive the downlink PPDU based on the HE-SIG A 905, the STA may configure a network allocation vector (NAV).

Referring to the bottom of FIG. 9, a PPDU format for DL MU OFDMA transmission is disclosed. According to an embodiment of the present invention, the AP may transmit a downlink frame or a downlink PPDU to a plurality of STAs using a PPDU format for DL MU OFDMA transmission. Each of the plurality of downlink PPDUs may be transmitted to each of the plurality of STAs through different transmission resources (frequency resources or spatial streams). The previous field of the HE-SIG B 945 on the PPDU may be transmitted in duplicated form in each of different transmission resources. The HE-SIG B 945 may be transmitted in encoded form on all transmission resources. The field after the HE-SIG B 945 may include individual information for each of the plurality of STAs that receive the PPDU.

For example, the HE-SIG A 935 may include identification information about a plurality of STAs to receive downlink data and information about a channel on which downlink data of the plurality of STAs are transmitted.

When the fields included in the PPDU are transmitted through each of the transmission resources, the CRC for each of the fields may be included in the PPDU. On the contrary, when a specific field included in the PPDU is encoded and transmitted on all transmission resources, the CRC for each field may not be included in the PPDU. Thus, overhead for CRC can be reduced.

Likewise, the PPDU format for DL MU transmission may be encoded based on an IFFT size different from that of the HE-STF 955 and the field after the HE-STF 955. Accordingly, when the STA receives the HE-SIG A 935 and the HE-SIG B 945, and is instructed to receive the PPDU based on the HE-SIG A 935, the STA has an FFT size from the HE-STF 955. Can be changed to perform decoding on the PPDU.

Referring to FIG. 10, the wireless device 1400 may be an STA that may implement the above-described embodiment, and may be an AP 1000 or a non-AP station (or STA) 1050.

The AP 1000 includes a processor 1010, a memory 1020, and an RF unit 1030.

The RF unit 1030 may be connected to the processor 1010 to transmit / receive a radio signal.

The processor 1010 may implement the functions, processes, and / or methods proposed in the present invention. For example, the processor 1010 may be implemented to perform the operation of the AP according to the above-described embodiment of the present invention. The processor may perform the operation of the AP disclosed in the embodiments of FIGS. 1 to 9.

For example, the processor 1010 may be implemented to transmit an RTS frame for medium protection to the STA, receive a CTS frame from the STA in response to the RTS frame, and transmit a data frame to the STA in response to the CTS frame. Can be.

The RTS frame is included in the first PPDU generated based on the first IFFT size, the data frame is included in the second PPDU generated based on the second IFFT size, and the second IFFT size may be larger than the first IFFT size. have. The data frame may be transmitted based on a transmission range determination parameter determined based on a difference between the second IFFT size and the first IFFT size.

The STA 1050 includes a processor 1060, a memory 1070, and a radio frequency unit 1080.

The RF unit 1080 may be connected to the processor 1060 to transmit / receive a radio signal.

The processor 1060 may implement the functions, processes, and / or methods proposed in the present invention. For example, the processor 1060 may be implemented to perform the operation of the STA according to the above-described embodiment of the present invention. The processor may perform an operation of the STA in the embodiment of FIGS. 1 to 9.

For example, the processor 1060 may be implemented to receive CCA threshold information for receiving a data frame and CCA threshold information for the RTS frame and to perform detection for the data frame and the RTS frame. In addition, the processor 1060 may be implemented to transmit the CTS frame with the same MCS index and transmission power as the RTS frame. When the STA transmits the RTS frame and the data frame, the processor 1060 may perform the same operation as the processor 1010.

Processors

1010 and 1060 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, data processing devices and / or converters to convert baseband signals and wireless signals to and from each other. The

memories

1020 and 1070 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media and / or other storage devices. The

RF unit

1030 and 1080 may include one or more antennas for transmitting and / or receiving a radio signal.

When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in the

memory

1020, 1070 and executed by the

processor

1010, 1060. The

memories

1020 and 1070 may be inside or outside the

processors

1010 and 1060 and may be connected to the

processors

1010 and 1060 by various well-known means.

Claims

The method of transmitting a frame in a WLAN,
Transmitting, by an access point (AP), a request to send (RTS) frame for media protection to a station (STA);
Receiving, by the AP, a clear to send (CTS) frame from the STA in response to the RTS frame; And
And transmitting, by the AP, a data frame to the STA in response to the CTS frame.
The RTS frame is included in a first physical layer protocol data unit (PPDU) generated based on a first inverse fast fourier transform (IFFT) size.
The data frame is included in a second PPDU generated based on a second IFFT size,
The second IFFT size is larger than the first IFFT size,
The data frame is transmitted based on a transmission range determination parameter determined based on a difference between the second IFFT size and the first IFFT size.
The method of claim 1,
The transmission range determination parameter includes a first modulation and coding scheme (MCS) index for modulation and coding of the data frame,
Wherein the first MCS index is greater than a second MCS index for modulation and coding of the RTS frame.
The method of claim 1,
The transmission range determination parameter comprises a first clear channel assessment (CCA) threshold for receipt of the data frame,
Wherein the first CCA threshold is greater than a second CCA threshold for receiving the RTS frame.
The method of claim 1,
The transmission range determination parameter includes a first transmission power for transmission of the data frame,
Wherein the first transmit power is less than a second transmit power for transmission of the RTS frame.
The method of claim 1,
The AP further comprises transmitting a transmission range synchronization frame on a broadcast basis,
The transmission range synchronization frame includes the transmission range determination parameter,
The transmission range determination parameter includes a CCA threshold setting field,
The CCA threshold setting field includes information on a first CCA threshold for receiving the RTS frame and information on a second CCA threshold for receiving the data frame.
An access point (AP) for transmitting a frame in a WLAN,
A radio frequency (RF) unit implemented to transmit or receive a radio signal; And
A processor operatively connected to the RF unit,
The processor transmits a request to send (RTS) frame for media protection to a station (STA),
Receiving a clear to send (CTS) frame from the STA in response to the RTS frame,
In response to the CTS frame is implemented to transmit a data frame to the STA,
The RTS frame is included in a first physical layer protocol data unit (PPDU) generated based on a first inverse fast fourier transform (IFFT) size.
The data frame is included in a second PPDU generated based on a second IFFT size,
The second IFFT size is larger than the first IFFT size,
The data frame is transmitted based on a transmission range determination parameter determined based on a difference between the second IFFT size and the first IFFT size.
The method of claim 6,
The transmission range determination parameter includes a first modulation and coding scheme (MCS) index for modulation and coding of the data frame,
Wherein the first MCS index is greater than a second MCS index for modulation and coding of the RTS frame.
The method of claim 6,
The transmission range determination parameter comprises a first clear channel assessment (CCA) threshold for receipt of the data frame,
Wherein the first CCA threshold is greater than a second CCA threshold for receiving the RTS frame.
The method of claim 6,
The transmission range determination parameter includes a first transmission power for transmission of the data frame,
The first transmission power is characterized in that less than the second transmission power for the transmission of the RTS frame.
The method of claim 6,
The processor is implemented to transmit transmission range synchronization frame on a broadcast basis,
The transmission range synchronization frame includes the transmission range determination parameter,
The transmission range determination parameter includes a CCA threshold setting field,
The CCA threshold setting field includes information on a first CCA threshold for receiving the RTS frame and information on a second CCA threshold for receiving the data frame.